This invention relates to a control device for internal combustion engines and more particularly to an improved event timing arrangement for an internal combustion engine.
In internal combustion engines, a number of events which occur in the combustion chamber or other portions of the engine are controlled at a specific timing with respect to the cycle of the engine. If the engine is a reciprocating engine, the timing is controlled in relation to the respective position of the piston in the combustion chamber. Normally, the timings are determined from the top dead center position. Similar timing controls are employed in rotary engines which operate on a cycle and again the timing is usually based upon timings relative to the time when the combustion chamber is at its minimum volume, corresponding to top dead center of the piston of a reciprocating engine. Normally all timing events are based upon the angular rotation of the crankshaft or engine output shaft relative to top dead center.
A triggering arrangement for the timing mechanism is provided which is designed so as to provide an output signal when the engine is at its top dead center or minimum volume condition. These timing devices normally include a toothed wheel that is driven by the engine output shaft and which cooperates with a sensor coil mounted in a fixed relationship to the output shaft. Obviously, there are a number of variations which can occur in both the mounting of the toothed wheel and the mounting of the sensor coil. These positional variations can cause all of the timed events to occur at an imprecise time or engine output shaft angular relationship, with resulting deterioration in engine performance.
In addition to these variations, the mounting of the piston relative to the engine output shaft in a reciprocating engine or the rotary member associated with the output shaft in a rotary engine relative to the output shaft can vary because of a number of reasons. Therefore, even if the toothed wheel and sensor coil are accurately located relative to each other, there still can be variations in timing which are undesirable.
It is, therefore, a principle object to this invention to provide an improved event timing arrangement for an internal combustion engine.
It is a further object to this invention to provide an improved timing arrangement for an internal combustion engine wherein the timing signal can be adjusted in response to the measured parameters of the engine.
It is a further object to this invention to provide an improved method for adjusting the timing of an internal combustion engine.
The timed events can be those of many different types. For example, in fuel injected engines, in addition to controlling accurately the timing of injection it is extremely important to accurately control the quantity of fuel injected in accordance with the air inducted in order to achieve the optimum fuel/air ratio for a given operating condition of the engine.
Various devices have been proposed for measuring the air flow in an induction system of an engine to control the amount of fuel injected. Conventionally, such air flow measuring devices have been large and complicated, and have been positioned in the induction system, normally upstream of the point of discharge of the fuel. In one type of flow detector, a flap type arrangement is provided in the intake passage and has a member that swings open to an amount that is determined by the air flow. The angular position of this detector is then measured and used to provide an air flow signal for the fuel injection system. Alternatively, vortex type air flow meters have been positioned in the induction system for determining air flow. Still another type of measuring device employs a hot wire anemometer which provides an electrical resistance wire interposed in the air stream to have its resistance vary in relation to the speed, i.e., cooling effect, of the air flowing through the induction system. The use of such flow meters in the induction system has several disadvantages.
In the first instance, the provision of an air flow measuring device in the induction system can oftentimes reduce the volumetric efficiency of the induction system. Furthermore, such devices substantially increase the size of the induction system. Also, devices of the type aforementioned are not particularly efficient with engines having a low number of cylinders or specifically with single cylinder engines due to the pulsations in the intake flow. Although such pulsations may be reduced to some extend through the use of a plenum chamber, this adds still further to the size of the induction system. Furthermore, if the flow meter is used in conjunction with the internal combustion engine of an outboard motor or other marine application, there is a high likelihood of corrosion in the moving components of the flow meter due to the salt in the atmosphere.
In U.S. Pat. No. 4,446,833 to Matsushita et al., and assigned to the assignee hereof, there is disclosed a control for a fuel injection system that has none of the foregoing disadvantages. The system disclosed in that patent senses the pressure in the crankcase of a two-cycle engine and uses the sensed pressure to measure air flow and control the amount of fuel injected. It has been found that the pressure in the crankcase, if accurately measured, is indicative of the amount of air induced.
Japanese Provisional Patent Publication Sho59-5875 discloses an engine wherein the air intake amount, for determining a proper amount of fuel for injection, is determined by making two separate pressure measurements during each crankshaft rotation. A value for the air intake amount is obtained by measuring the air pressure at a crankshaft position near the scavenging port opening timing, which is representative of the mass of the air remaining in the crank chamber at the beginning of the scavenging stroke; and, also, measuring the air pressure at a crankshaft position near the scavenging port closing timing, which is representative of the mass of the air remaining in the crank chamber at the termination of the scavenging stroke.
With the systems just described, it is extremely important that each pressure measurement that is made, be made at a precise predetermined timing, indicative of the crank angle position, by the particular timing detecting means employed; for example, a crank angle wheel and sensor coil arrangement.
For the reasons noted above during the actual operation of an engine, it may occur that the timing detecting means is unable to deliver a precise timing signal due to manufacturing and/or assembling variations of the component parts. Such variations may cause the measured timing to deviate from the true, and desired, timing measurement. When the timing detecting means is unable to ascertain and provide the true timing signal, any crank chamber pressure measurement relying on such timing detecting means will consequently be in error. That is, the desired crank chamber pressure measurements cannot be ascertained, thereby causing an error in any calculated air intake amount which, in turn, results in a decreased accuracy in fuel injection amount control.
In addition to the timing of the pressure measurements in order to measure air flow, it is, as has been discussed above, extremely important to insure that the timing of beginning of fuel injection occur at a precise engine output shaft angle. Thus, with a fuel injection system it is important not only to be able to measure crankshaft angle position accurately so as to determine the amount of fuel required, but also so as to insure the accurate timing of fuel injection relative to the position of the piston.
In addition to the timing of the fuel injection of an engine, there are a number of other events which must be accurately timed. For example, the timing of spark firing in spark ignited engines is also extremely critical. The methods which have been employed for controlling spark timing are similar to those discussed above in that they include a timing wheel driven by the engine output shaft and in an associated sensor, with the possible defects aforenoted.
It is, therefore, a still further object to this invention to provide an improved timing arrangement and method for determining the timing of an event in an internal combustion engine which can be extremely accurate and adjusted to accommodate specific manufacturing variations in a given engine.
It is a further object to this invention to provide an improved fuel injection system for an internal combustion engine.
It is another object to this invention to provide an improved spark ignition system for an internal combustion engine.